1. Field of the Invention
The present invention relates to fuel control of an internal combustion engine, and more particularly to a device for correcting a fuel injection amount of an internal combustion engine, which performs feedback control according to an output value of an oxygen sensor provided in an exhaust pipe, and to a control apparatus for an internal combustion engine employing the device.
2. Description of the Related Art
A conventional fuel injection control apparatus for an internal combustion engine performs control with a control gain that is set larger than usual until initial inversion occurs after the start of O2 feedback (e.g., see JP 2003-232248 A).
In this conventional fuel injection control apparatus for an internal combustion engine, the control gain is set larger than usual until initial inversion occurs after the start of O2 feedback. The speed of following a stoichiometric air-fuel ratio (i.e., a theoretical air-fuel ratio) after the start of O2 feedback is thereby increased.
Combustion is unstable and the range allowing combustion on a lean side of an air-fuel ratio A/F is narrow when an internal combustion engine is at a low temperature. For instance, although combustion is possible at an air-fuel ratio of A/F=17 or less after an internal combustion engine has warmed up, combustion is impossible at an air-fuel ratio of A/F=15 or more when an internal combustion engine is cold.
Even if the air-fuel ratio A/F is within a range allowing combustion, the torque of an internal combustion engine drastically decreases when the air-fuel ratio A/F shifts to the lean side. Therefore, there is a problem in that the RPM of an internal combustion engine sharply decreases when a large feedback gain is set to shift the air-fuel ratio A/F to the lean side at an early stage.
Furthermore, there is another problem in that misfire, which leads to engine stall in some cases, is caused when the combustion state of an internal combustion engine exceeds a combustion limit (on the lean side).
Immediately after the start of an internal combustion engine as well, combustion is unstable and the feedback is set large as in a period in which the internal combustion engine is cold. Therefore, there is a problem in that a decrease in RPM, misfire, engine stall, and the like are caused when an attempt is made to shift the air-fuel ratio to the lean side at an early stage.
The range allowing combustion on the lean side of the air-fuel ratio A/F is narrower in a low-load operation range than in a high-load operation range, and, in particular, the feedback gain is set large especially in the low-load operation range immediately after the start of an internal combustion engine as well. Therefore, there is a problem in that a decrease in RPM, misfire, engine stall, and the like are caused when an attempt is made to shift the air-fuel ratio to the lean side at an early stage.